APPARATUS AND METHOD FOR TRANSFERRING HEAT

Abstract

An apparatus is for transferring heat. The apparatus has a heat transfer circuit with a heat transfer medium. The heat transfer circuit has: a heat receipt path having a first heat exchanger; a heat dispatch path having a compressor device and a second heat exchanger; and an intermediate path having an ejector device and a separator. A primary first heat exchanger is arranged: a) in a primary heat receipt path in the heat receipt path and connected to the separator; or b) in the separator. A secondary heat receipt path is arranged with a secondary first heat exchanger connected to the suction inlet of the ejector device. A method is for transferring heat using the apparatus.

Description

INTRODUCTION

The invention relates to an apparatus and a method for transferring heat comprising a heat transfer circuit with a heat transfer medium. The heat transfer circuit comprises a heat receipt path comprising a first heat exchanger for transferring heat to the heat transfer medium, a heat dispatch path comprising a compressor device and a second heat exchanger for transferring heat away from the heat transfer medium; and an intermediate path between the receipt path and the dispatch path. The intermediate path comprises an ejector device and a separator. The ejector device comprises a main inlet connected to the dispatch path, a suction inlet, and main outlet connected to the separator. The separator is configured to receive heat transfer medium from the ejector device and to provide heat transfer medium to the receipt and dispatch paths.

PRIOR ART

Cooling, i.e. the transfer of heat from one location to another, is required in a vast range of applications, for example for chillers and air conditioning of buildings and for cooling refrigerators and freezers. A common cooling method relies on vapour-compression refrigeration cycle, wherein a heat transfer medium, typically called a refrigerant, changes phase during the refrigeration cycle. A basic vapour-compression refrigeration system typically comprises a compressor, wherein the heat transfer medium in the gaseous phase is compressed into a superheated gaseous phase. This superheated gaseous phase then enters a condenser, wherein the superheat is transferred away from the heat transfer medium, and the gaseous heat transfer medium is condensed into a liquid. This liquid then passes a flow restriction, e.g. an expansion valve, wherein the pressure decreases such that a part of the liquid vaporises and thus cools down. This now cooled mixture of gaseous and liquid heat transfer medium subsequently enters an evaporator, wherein the remaining portion of the heat transfer medium in liquid phase vaporises by transferring heat to the heat transfer medium from the system which should be cooled, e.g. a refrigerator. The gaseous heat transfer medium then enters the compressor again for the cycle to restart.

The choice of heat transfer medium is important for the performance of the refrigeration system. A typically used heat transfer medium is Freon, which comprises haloalkanes. As haloalkanes may contribute to the depletion of the ozone layer, other alternatives which reduce the ozone depletion are being used in newer cooling systems, for example hydrofluorocarbons and hydrochlorofluorocarbons. However, these refrigerants all have a large global warming potential, so refrigerants which are better for the environment are being investigated.

A possible substitute for the refrigerants used today is carbon dioxide, which is nontoxic, cheap, has a low global warming potential, and may be a suitable refrigerant for most applications. On the downside carbon dioxide needs a relatively high pressure and has a low critical temperature of around 31° C., which may cause difficulties in warmer climates. Additionally, the cycle loses a large degree of energy due to irreversibility in the carbon dioxide expansion process when it goes from a supercritical region to the two-phase region.

To make use of some of the energy lost in the carbon dioxide expansion process, it has been proposed to include an ejector in the vapour-expansion refrigeration cycle after the condenser/gas cooler. An ejector is a device which comprises a main inlet, a main outlet, and a suction inlet, and which is constructed in such a way that a suction pressure is created in the suction inlet when a flow into the main inlet is established. The heat transfer medium from the main inlet and the suction inlet is mixed inside the ejector. A gas-liquid separator is also included after the ejector. The separator separates the heat transfer medium into gaseous carbon dioxide, which enters the compressor and starts a new cycle, and liquid carbon dioxide, which goes through the expansion valve and the evaporator as described above, before entering the ejector suction inlet. A diagram of this prior art ejector-expansion cycle is shown in FIG. 1. The overall effect of the process is to decrease the energy needed for the compressor compared to the cycle without the ejector, as some of the energy lost in the expansion process is used to drive the refrigeration cycle. This process works well at high cooling need, however, at low cooling need the system will have difficulties cooling since the ejector requires a minimum flow through the main inlet to create a suction pressure in the suction inlet. It will therefore be difficult to regulate the cooling, the heat exchange will be unsteady, and the energy efficiency will decrease. Additionally, the system may risk a situation where the heat transfer medium in the separator becomes very cold and boils at low pressure and temperature, whereby the compressor cannot run as intended due to too low suction pressure. Thereby, no or insufficient flow will reach the ejector inlet to create a suction pressure at the suction inlet, so no heated heat transfer medium will pass from the evaporator to the separator to heat up the heat transfer medium in the separator. This situation may be referred to as a dead lock position.

“Transcritical CO₂ Refrigeration Cycle with Ejector-Expansion Device”, International Journal of Refrigeration, Volume 28, Issue 5, August 2005, Pages 766-773, Daqing Li, Eckhard A. Groll, discloses an apparatus and a method for transferring heat according to FIG. 1.

EP1327838A2, WO2012012488A1, US2004003608A1, and CN104359246A disclose other prior art devices for transferring heat.

SUMMARY OF THE INVENTION

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art. The object is achieved through features which are specified in the description below and in the claims that follow. The invention is defined by the independent patent claims, and the dependent claims define advantageous embodiments of the invention.

In particular, a first object of the invention is to provide an apparatus for transferring heat with improved efficiency at high heat transfer requirement. A second object of the invention is to provide an apparatus for transferring heat with improved stability at low heat transfer requirement. A third object of the invention is to provide an apparatus for transferring heat with reduced risk of going into a dead lock position. A fourth object of the invention is to provide the above improvements for an apparatus that is based on a heat exchange medium mainly comprising CO₂.

The above objects are achieved by means of an apparatus for transferring heat. The apparatus comprises a heat transfer circuit with a heat transfer medium, wherein the heat transfer circuit comprises: a heat receipt path comprising a first heat exchanger for transferring heat to the heat transfer medium; a heat dispatch path comprising a compressor device and a second heat exchanger for transferring heat away from the heat transfer medium; and an intermediate path between the receipt path and the dispatch path, which intermediate path comprises an ejector device and a separator, wherein the ejector device comprises a main inlet connected to the dispatch path, a suction inlet, and main outlet connected to the separator, and wherein the separator is configured to receive heat transfer medium from the ejector device and to provide heat transfer medium to the receipt and dispatch path.

The first heat exchanger comprises a primary first heat exchanger and a secondary first heat exchanger, and the apparatus is characterised in that: a) the heat receipt path further comprises a primary heat receipt path arranged with the primary first heat exchanger and connected to the separator without passing the ejector device; or b) the primary first heat exchanger is arranged in or in direct connection to the separator, wherein for both options a) and b) the heat receipt path further comprises a secondary heat receipt path arranged with the secondary first heat exchanger connected to the suction inlet of the ejector device, wherein the secondary heat receipt path further comprises an expansion device upstream of the secondary first heat exchanger. In an alternative embodiment, the heat receipt path may comprise both a primary heat receipt path arranged with the primary first heat exchanger and connected to the separator without passing the ejector device; and a primary first heat exchanger arranged in or in direct connection to the separator.

The effect of the apparatus is to transfer heat to the heat transfer medium at the first heat exchanger, and transfer heat away from the heat transfer medium at the second heat exchanger. The first heat exchanger and the second are separated from each other. The apparatus may cool or heat a space, for example for use as a water chiller unit or refrigerator or air condition in a house.

The heat transfer medium is conducted in the circuit by the compressor device. Typically, the compressor device may be a compressor which may compress the gaseous heat transfer medium, whereby the temperature of the gaseous heat transfer medium will increase. The heat transfer medium, which may at this stage be a superheated vapour, then enters the second heat exchanger, such as a gas cooler or a condenser, wherein heat will be transferred away from the heat transfer medium. The heat transfer medium will thereby cool down, and potentially condense fully or partially into a liquid. After the second heat exchanger, the heat transfer medium continues into the main inlet of the ejector device, where the heat transfer medium at least partially expands. If the flow through the ejector device is sufficiently high, a suction pressure may be created at the ejector suction inlet upon expansion of the heat transfer medium in the ejector.

The term “ejector device” shall be understood as a pump-like device that creates a suction at the suction inlet. The ejector device is also denoted ejector or injector. The suction is due to the internal shape of the ejector device.

After passing through the ejector device, the heat transfer medium, typically existing as a mixture of gaseous and liquid heat transfer medium, enters the separator, where the heat transfer medium is separated into a gaseous phase and liquid phase. The separator may for example be an accumulation tank, wherein the liquid may separate at the bottom due to gravity. From the separator, the heat transfer medium, typically as a liquid, is conducted to the heat receipt path and the first heat exchanger for transferring heat to the heat transfer medium. The first heat exchanger comprises the primary first heat exchanger and the secondary first heat exchanger, which for example are evaporators.

When the heat transfer medium reaches the primary first heat exchanger, either in the separator or in the primary heat receipt path, heat will be transferred to the heat transfer medium. If the primary first heat exchanger is in the primary heat receipt path and the heat transfer medium is in liquid form at this stage, it may at least partially vaporise into a gaseous phase, or typically a mixture of liquid and gaseous heat transfer medium. Optionally, more than one primary first heat exchanger may be connected in series in the primary heat receipt path, whereby more, or all, of the liquid may vaporise. The mixture may thereafter be returned to the separator without passing the ejector device. The term “without passing the ejector device” shall be understood as the heat transfer medium from the primary first heat exchanger being conducted to the separator without being acted upon by the ejector device. If the primary first heat exchanger is positioned in or in direct connection to the separator, heat may be transferred directly to the heat transfer medium in the separator, possible causing some of the heat transfer medium in the liquid state to vaporise into a gaseous phase.

In the secondary heat receipt path, the heat transfer medium, typically as a liquid, pass the expansion device, such as an expansion valve, a capillary tube, or another kind of pressure restriction, where it may expand at least partially into a mixture of gaseous and liquid heat transfer medium.

Upon expansion, the temperature of the heat transfer medium will decrease. The heat transfer medium then enters the secondary first heat exchanger, wherein heat will be transferred to the heat transfer medium.

The expansion device is arranged upstream of the secondary first heat exchanger. The term “upstream of the secondary first heat exchanger” relates to the fact that the expansion device receives the heat transfer medium in the secondary heat receipt path prior to the secondary first heat exchanger.

Due to the expansion device the heat transfer medium will have a lower temperature at the secondary first heat exchanger than at the primary first heat exchanger. Accordingly, the primary first heat exchanger and the secondary first heat exchanger handle separate portions of transferring heat to the heat transfer medium in the heat receipt path.

The flow of the heat transfer medium in the secondary heat receipt path is caused by the suction pressure at the suction inlet of the ejector. The heat transfer medium from the secondary heat receipt path will therefor pass through the suction inlet of the ejector and out of the ejector outlet into the separator. From the separator, the heat transfer medium, typically in gaseous phase, is then passing to the compressor device for the next cycle.

By including a primary first heat exchanger directly in the separator or in a primary heat receipt path which bypasses the ejector, and the secondary first heat exchanger in a secondary heat receipt path which passes the ejector, the problem with the unsteady cooling at low cooling requirement, which is present without primary first heat exchanger positioned in the primary heat receipt path or in or direct connection to the separator, will be avoided. At low cooling requirement the compressor device will run at reduced capacity, and the ejector device will not have sufficient flow through the main inlet to create a suction pressure at the suction inlet. The ejector device will therefore substantially not cause any heat transfer medium to flow through the secondary heat receipt path. However, the heat transfer medium may still receive heat at the primary first heat exchanger if this is positioned in the separator or in the primary heat receipt path. The apparatus will therefore provide more stable heat transfer at low heat transfer need and more effective heat transfer at high heat transfer requirement than prior art apparatuses are capable of. Additionally, the risk of going into a dead lock position as described above is eliminated. If the primary first heat exchanger is positioned in or in direct connection to the separator, the heat transfer medium in the separator may receive heat directly from the primary first heat exchanger even if no heat transfer medium is flowing through the secondary heat receipt path. If the primary first heat exchanger is positioned in the primary heat receipt path, heated heat transfer medium from the primary first heat exchanger may enter the separator also if the flow through the ejector device is insufficient to create a suction pressure at the suction inlet of the ejector device. Therefore, a primary first heat exchanger positioned in or in direct connection to the separator, or in the primary heat receipt path, will both provide a more stable heat transfer at low heat transfer need and therefore avoid the risk of going into a dead lock position.

According to an embodiment of the invention, the primary first heat exchanger and the secondary first heat exchanger are configured to receive a further heat transfer medium for transferring heat to the heat transfer medium.

The heat from the further heat transfer medium is transferred to the heat transfer medium in the heat receipt path by means of the primary first heat exchanger and secondary first heat exchanger. By means of this configuration of the primary and secondary first heat exchangers it is possible to cool two separate further heat transfer mediums at different temperatures, or one further heat transfer medium in two steps by leading the fluid past the primary and secondary first heat exchanger in series. In this way the further heat transfer medium will be cooled partially at the primary first heat exchanger and partially at the secondary first heat exchanger.

The further heat transfer medium may for example be a liquid, or it may alternatively be hot air or gas which is passed across the surfaces of the primary and secondary first heat exchangers in series. In this way the hot air or gas may be partially cooled at the primary first heat exchanger and further cooled at the secondary first heat exchanger. The further heat transfer medium is for example water.

The flow of the heat transfer medium in the secondary heat receipt path may be caused by the suction pressure at the suction inlet of the ejector. The heat transfer medium from the secondary heat receipt path will therefor pass through the suction inlet of the ejector device and out of the ejector outlet into the separator. From the separator, the heat transfer medium, typically in the gaseous phase, may be passed to the compressor device for the next cycle.

According to an embodiment of the invention, the heat transfer medium mainly comprises CO₂, which is better for the environment than most other suitable heat transfer mediums. The apparatus may also be particularly beneficial if the heat transfer medium is CO₂, since it avoids or decreases some of the drawbacks experienced with using CO₂ as the heat transfer medium in prior art apparatuses. Preferably, the heat transfer medium consists of CO₂, and possible impurities.

According to an embodiment of the invention, the apparatus comprises at least one sensor for identifying a physical quantity dependent on a state of the heat transfer medium and a control unit, wherein the at least one sensor is positioned downstream of the secondary first heat exchanger and upstream of the suction inlet of the ejector device, and the control unit is adapted to receive information from the at least one sensor and control the expansion device on the basis of said information so that the heat transfer medium is mainly in the gaseous state after passing the secondary first heat exchanger.

The control unit controls the flow of the heat transfer medium through the secondary first heat exchanger by means of controlling the expansion device based on the information from the sensor or sensors so as to ensure that all the liquid or essentially all liquid of the heat transfer medium is evaporated in the secondary first heat exchanger, such that only gaseous heat transfer medium enters the suction inlet of the ejector device, as the ejector device is configured for accepting a gaseous heat transfer medium at the suction inlet. Liquid at the suction inlet of the ejector device may potentially cause problems. The sensor may for example be a temperature sensor, a pressure sensor, an optical sensor, or a combination, as the state of the heat transfer medium may be reliably determined by these properties.

According to an embodiment of the invention, the primary first heat exchanger is positioned in the primary heat receipt path and lower in elevation than the separator, whereby gravity may cause the liquid heat transfer medium in the separator to be led into the primary first heat exchanger. This will assure flow of the heat transfer medium through the primary first heat exchanger without any additional pump. Alternatively, a pump device may be used.

According to an embodiment of the invention, the heat dispatch path comprises an internal heat exchanger for exchanging heat between the heat transfer medium flowing upstream of the compressor device and downstream of the second heat exchanger. This may increase the efficiency of the apparatus, as there may typically remain a difference in temperature of the heat transfer medium downstream of the second heat exchanger and upstream of the compressor device. The internal heat exchanger may therefore cause heat to be transferred from the heat transfer medium flowing downstream of the second heat exchanger to the heat transfer medium flowing upstream of the compressor device. At this position a high temperature may be beneficial, as it may decrease the work needed to be performed by the compressor device to raise the pressure sufficiently. It will also prevent that the compressor will operate with at a non-optimal low temperature at the inlet of the compressor.

According to an embodiment of the invention, the apparatus may furthermore comprise at least one additional path connecting the heat receipt path downstream of the separator and upstream of the first heat exchanger to the heat dispatch path downstream of the separator and upstream of the compressor device, wherein the additional path comprises a flow restriction, e.g. an expansion device. This additional path and flow restriction may be particularly beneficial if the compressor device is lubricated by lubricating oil, since the compressor device may in that situation typically let out a small amount of lubricating oil through the outlet of the compressor device, and the lubricating oil may thereby end up in the separator in the liquid phase of the heat transfer medium. By including the additional path with a flow restriction, a small amount of liquid heat transfer medium including oil may continuously be led to the heat dispatch path upstream of the compressor device. The heat transfer medium may vaporise through the flow restriction while the lubricating oil will run into the compressor. An internal heat exchanger as described above may be included to ensure that all heat transfer medium is vaporised before the compressor device.

The above objects are furthermore achieved by means of a method for transferring heat by means of an apparatus according to any of the claims 1-8. The method comprises the steps of:

• • receiving information from at least one sensor for identifying a state of the heat transfer medium downstream of the secondary first heat exchanger and upstream of the suction inlet of the ejector device, and
  • adjusting the flow of the heat transfer medium through the expansion device on the basis of the information from the at least one sensor so that the heat transfer medium is mainly in the gaseous state after passing the secondary first heat exchanger.

Preferably, the flow of the heat transfer medium is adjusted so that more than 90% of the heat transfer medium is in the gaseous state, more preferably more than 95% of the heat transfer medium.

The above objects are furthermore achieved by means of use of an apparatus according to any of the claims 1-8.

BRIEF DESCRIPTION OF DRAWINGS

In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:

FIG. 1 shows a diagram of a heat transfer circuit of an apparatus for transferring heat according to prior art;

FIG. 2 shows a diagram of a heat transfer circuit of an apparatus for transferring heat according to an embodiment of the invention;

FIG. 3 shows a diagram of a heat transfer circuit of the apparatus according to a further embodiment of the invention; and

FIG. 4 shows a diagram of a heat transfer circuit of an apparatus for transferring heat according to an even further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, the reference numeral 10 indicates a heat transfer circuit comprising a heat transfer medium. Identical reference numerals indicate identical or similar features in the drawings. The drawings are presented in a simplified and schematic manner, and the features therein are not necessarily drawn to scale. The short arrows adjacent and parallel to the lines in the diagrams indicate the flow direction of the heat transfer medium in the circuit.

FIG. 1 shows a heat transfer circuit 10 comprising a heat transfer medium according to prior art. The heat transfer circuit 10 comprises a heat receipt path 11, which comprises a first heat exchanger 6 for transferring heat to the medium, and a heat dispatch path 12, which comprises a second heat exchanger 2 for transferring heat away from the medium. Furthermore, the heat transfer circuit 10 comprises an intermediate path 13 between the heat receipt path 11 and heat dispatch path 12, which intermediate path 13 comprises an ejector device 3 and a separator 4. In the heat transfer circuit 10, the compressor 1 compresses the heat transfer medium (present in a gaseous state), whereby the temperature increases. Upon entering the second heat exchanger 2, for example a condenser, the gas cools down and condenses at least partially into a liquid. The heat transfer medium continues through the main inlet 31 of the ejector device 3, thereby creating a suction pressure at the suction inlet 32, before leaving the ejector 3 through the main outlet 33 and entering the separator 4. In the separator 4, the heat transfer medium is separated into a gaseous phase 41 and a liquid 42. From the separator, the heat transfer medium in the liquid state is then passed through an expansion device 5, for example an expansion valve, wherein it expands at least partially into a vapour, and thereby cools further down. The heat transfer medium, typically present as a vapour-liquid mixture, then enters the first heat exchanger 6, wherein heat is transferred to the heat transfer medium, e.g. from a further heat transfer medium in an external circuit 14. The further heat transfer medium is for example water.

The heat transferred to the heat transfer medium may cause the remaining heat transfer medium in the liquid phase to vaporise. Thereby only vapour will continue to the suction inlet 32 of the ejector 3. Also, from the separator, the heat transfer medium in the gaseous phase is passed to the compressor 1 for the cycle to continue. This prior art circuit has the problem that at low cooling need the compressor 1 will run at low power, whereby the pressure at the main inlet 31 of the ejector 3 may be too low to cause a suction pressure at the suction inlet 32 of said ejector 3. This circuit will therefore result in unsteady cooling since the compressor 1 will have to run at high power for shorter intervals at low cooling need, which will furthermore be inefficient.

FIG. 2 shows a diagram of a heat transfer circuit 10 of an apparatus 50 for transferring heat according to an embodiment of the invention. Compared to prior art, the heat receipt path 11 comprises a primary heat receipt path 11a comprising a primary first heat exchanger 7, and a secondary heat receipt path 11b comprising a secondary first heat exchanger 6 and a controllable expansion device 5, e.g. an expansion valve. The primary heat exchange path 11a receives liquid heat transfer medium from the separator 4 and returns a mixture of liquid and gaseous heat transfer medium to the same separator 4 without passing the ejector 3. The secondary heat receipt path 11b receives liquid heat transfer medium from the separator 4 and provides gaseous heat transfer medium to the suction inlet 32 of the ejector 3.

Thus, at low cooling need when the compressor 1 runs at low capacity, the heat transfer medium will still run through the primary heat receipt path 11a, whereby heat will be transferred to the heat transfer medium through the primary first heat exchanger 7, since the primary heat receipt path 11a is not connected to the suction inlet 32 of the ejector 3. The heat transfer circuit 10 of the invention thus avoids the problems with the prior art embodiment which may arise at low cooling requirement. When the cooling requirement increases and the compressor 1 runs with higher capacity, a suction pressure at the suction inlet 32 of the ejector 3 is established, thus ensuring flow of the heat transfer medium through the secondary receipt path 11b.

Upon expansion of the heat transfer medium through the expansion device 5, the temperature of the heat transfer medium will decrease. The secondary first heat exchanger 6 will therefore be able to cool the further heat transfer medium in the external circuit 14 to a lower temperature than the primary first heat exchanger 7.

The apparatus 50 further comprises a control unit 60 and at least one sensor 62 for measuring a physical quantity dependent on a state of the heat transfer medium. The at least one sensor 62 is positioned downstream of the secondary first heat exchanger 6 and upstream of the suction inlet 32 of the ejector device 3.

The control unit 60 is connected to the at least one sensor 62 and is adapted to receive information from the at least one sensor 62. The control unit 60 comprises a logic unit 70 and a memory unit 72. The received information from the at least one sensor 62 is adapted to be stored in the memory unit 72. The logic unit 70 is configured to process the stored information from the sensor 62 and determining the state of the heat transfer medium downstream of the secondary first heat exchanger 6 and upstream of the suction inlet 32 of the ejector device 3.

The control unit 60 is connected to the expansion device 5 and comprises means for transmitting control information to the expansion device 5 for adjusting the flow of the heat transfer medium through the expansion device 5 so that the heat transfer medium is mainly in the gaseous state after passing the secondary first heat exchanger 6.

In FIG. 2 the external circuit 14 runs through the primary 7 and secondary 6 first heat exchangers in series, thus cooling the further heat transfer medium in two steps. The two first heat exchangers 6,7 may alternatively cool two separate further heat transfer mediums in parallel.

FIG. 3 shows a diagram of a heat transfer circuit 10 of the apparatus 50 according to a further embodiment of the invention. The heat transfer circuit 10 in FIG. 3 differs from the heat transfer circuit 10 in FIG. 2 in that the heat transfer circuit 10 additionally comprises an internal heat exchanger 8 in the heat dispatch path 12, and an additional path which comprises a flow restriction 9 and connects the heat receipt path 11 downstream of the separator 4 and upstream of the first heat exchangers 6,7 to the heat dispatch path 12 downstream of the separator 4 and upstream of the compressor device 1. This heat transfer circuit 10 is especially beneficial if the compressor device 1 is lubricated by lubricating oil, which may exit said compressor device 1 and enter the separator 4, where it may be mixed into the liquid part 42 of the heat transfer medium. The flow restriction 9 is included to bleed a small amount of liquid heat transfer medium including lubricating oil into the heat dispatch path 12 to return the oil to the compressor device 1. The internal heat exchanger 8 ensures that all the liquid heat transfer medium vaporises before entering the compressor device 1 and that the heat transfer medium is not too cold for optimal functioning of the compressor device 1.

FIG. 4 shows a diagram of a heat transfer circuit 10 of the apparatus 50 according to an even further embodiment of the invention. This embodiment is similar to the embodiment shown in FIG. 2, but in the embodiment shown in FIG. 4 the primary first heat exchanger 7 is arranged in the separator 4 instead of the in a primary heat receipt path 11a (as shown in FIG. 2). The arrangement shown in FIG. 4 provides a similar technical effect as the arrangement shown in FIG. 2. At low cooling need when the compressor 1 runs at low capacity, no heat transfer medium will be conducted through the secondary heat receipt path 11b, as the flow through the ejector 3 is too low to create a suction pressure at the suction inlet 32. However, as the primary first heat exchanger 7 is positioned in the separator 4, heat will still be transferred to the heat transfer medium in the separator 4. This will cause some of the heat transfer medium in the liquid phase to vaporise to the gaseous phase, which will be available for the compressor 1 via the heat dispatch path 12. The heat transfer circuit 10 of the invention therefore avoids the problems of the prior art embodiment which may arise at low cooling requirement. When the cooling requirement increases and the compressor 1 runs with higher capacity, a suction pressure at the suction inlet 32 of the ejector 3 is established, and flow of the heat transfer medium through the secondary receipt path 11b will be established.

The invention also relates to a method of controlling the apparatus 50. The method comprises an initial step of receiving information from the sensor 62 for identifying a state of the heat transfer medium downstream of the secondary first heat exchanger 6 and upstream of the suction inlet 32 of the ejector device 3.

In a subsequent step the method comprises adjusting the flow of the heat transfer medium through the expansion device 5 on the basis of the information from the sensor 62 so that the heat transfer medium is mainly in the gaseous state after passing the secondary first heat exchanger 6. Thereby, it is assured that the suction inlet of the ejector device 3 receives the heat transfer medium mainly in the gaseous state.

Preferably, the flow of the heat transfer medium is adjusted so that more than 90% of the heat transfer medium is in the gaseous state, more preferably more than 95% of the heat transfer medium.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps which are not stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

Claims

1. An apparatus for transferring heat, the apparatus comprising a heat transfer circuit with a heat transfer medium, wherein the heat transfer circuit comprises:

a heat receipt path comprising a first heat exchanger for transferring heat to the heat transfer medium;

a heat dispatch path comprising a compressor device and a second heat exchanger for transferring heat away from the heat transfer medium; and

an intermediate path between the receipt path and the dispatch path, which intermediate path comprises an ejector device and a separator, wherein the ejector device comprises a main inlet connected to the dispatch path, a suction inlet, and main outlet connected to the separator, and wherein the separator is configured to receive heat transfer medium from the ejector device and to provide heat transfer medium to the heat receipt path and the heat dispatch path,

wherein the first heat exchanger comprises a primary first heat exchanger and a secondary first heat exchanger, wherein

a) the heat receipt path further comprises a primary heat receipt path arranged with the primary first heat exchanger and connected to the separator without passing the ejector device, or

b) the primary first heat exchanger is arranged in or in direct connection to the separator,

wherein for both options a) and b) the heat receipt path further comprises a secondary heat receipt path arranged with the secondary first heat exchanger connected to the suction inlet of the ejector device, wherein the secondary heat receipt path further comprises an expansion device upstream of the secondary first heat ex-changer.

2. The apparatus according to claim 1, wherein the heat transfer medium mainly comprises CO2.

3. The apparatus according to claim 1, wherein the apparatus comprises at least one sensor for identifying a physical quantity dependent on a state of the heat transfer medium and a control unit, wherein the at least one sensor is positioned downstream of the secondary first heat exchanger and upstream of the suction inlet of the ejector device, and the control unit is adapted to receive information from the at least one sensor and control the expansion device on the basis of said information so that the heat transfer medium is mainly in the gaseous state after passing the secondary first heat exchanger.

4. The apparatus according to claim 3, wherein the sensor is one of a temperature sensor, a pressure sensor and an optic sensor.

5. The apparatus according to claim 1, wherein the primary first heat exchanger is positioned lower in elevation than the separator.

6. The apparatus according to claim 1, wherein the primary heat receipt path further comprises a pump device for conducting the heat transfer medium through the primary first heat exchanger.

7. The apparatus according to claim 1, wherein the heat dispatch path comprises an internal heat exchanger for exchanging heat between the heat transfer medium flowing upstream of the compressor device and downstream of the second heat exchanger.

8. The apparatus according to claim 1, wherein the apparatus comprises an additional path connecting the heat receipt path downstream of the separator and upstream of the first heat exchanger to the heat dispatch path downstream of the separator and upstream of the compressor device, wherein the additional path comprises a flow restriction.

9. A method for transferring heat via an apparatus, the apparatus comprising a heat transfer circuit with a heat transfer medium, wherein the heat transfer circuit comprises:

a heat receipt path comprising a first heat exchanger for transferring heat to the heat transfer medium;

a heat dispatch path comprising a compressor device and a second heat exchanger for transferring heat away from the heat transfer medium; and

an intermediate path between the receipt path and the dispatch path, which intermediate path comprises an ejector device and a separator, wherein the ejector device comprises a main inlet connected to the dispatch path, a suction inlet, and main outlet connected to the separator, and wherein the separator is configured to receive heat transfer medium from the ejector device and to provide heat transfer medium to the heat receipt path and the heat dispatch path,

wherein the first heat exchanger comprises a primary first heat exchanger and a secondary first heat exchanger, wherein

a) the heat receipt path further comprises a primary heat receipt path arranged with the primary first heat exchanger and connected to the separator without passing the ejector device, or

b) the primary first heat exchanger is arranged in or in direct connection to the separator,

wherein for both options a) and b) the heat receipt path further comprises a secondary heat receipt path arranged with the secondary first heat exchanger connected to the suction inlet of the ejector device, wherein the secondary heat receipt path further comprises an expansion device upstream of the secondary first heat ex-changer, wherein the method comprises the steps of:

receiving information from at least one sensor for identifying a state of the heat transfer medium downstream of the secondary first heat exchanger and upstream of the suction inlet of the ejector device, and

adjusting the flow of the heat transfer medium through the expansion device on the basis of the information from the at least one sensor so that the heat transfer medium is mainly in the gaseous state after passing the secondary first heat exchanger.

10. (canceled)